text: /*
   * Copyright (c) Facebook, Inc. and its affiliates.
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  #pragma once
  
  #include <folly/logging/AsyncLogWriter.h>
  
  #include <vector>
  
  namespace folly {
  /**
   * An implementation of `folly::AsyncLogWriter` that writes log messages into a
   * file.
   *
   * See `folly::AsyncLogWriter` for details on asynchronous IO.
   */
  class AsyncFileWriter : public AsyncLogWriter {
   public:
    /**
     * Construct an AsyncFileWriter that appends to the file at the specified
     * path.
     */
    explicit AsyncFileWriter(folly::StringPiece path);
  
    /**
     * Construct an AsyncFileWriter that writes to the specified File object.
     */
    explicit AsyncFileWriter(folly::File&& file);
  
    ~AsyncFileWriter();
  
    /**
     * Returns true if the output steam is a tty.
     */
    bool ttyOutput() const override;
  
    /**
     * Get the output file.
     */
    const folly::File& getFile() const {
      return file_;
    }
  
   private:
    void writeToFile(std::vector<std::string>* ioQueue, size_t numDiscarded);
  
    void performIO(std::vector<std::string>* ioQueue, size_t numDiscarded)
        override;
  
    std::string getNumDiscardedMsg(size_t numDiscarded);
  
    folly::File file_;
  };
  } // namespace folly
  